Modeling the role of humic substances in the distribution of trace metals in selected ecosystems in Ghana
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Date
2015-07-12
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Abstract
The complexity of semi-natural ecosystems in terms of the composition and
chemical properties of the solid and solution phases has cause researchers to develop
intelligent and innovative ways of modeling and using the models to describe the
chemistry of metal distribution in natural environments. But a comprehensive model
that adequately describes the role humic substances play in trace metal distribution in
semi-natural ecosystems is absent. The colloidal properties and aggregation properties
at cloud point have not been effectively correlated with its cation binding properties.
In view of these the role of humic substances in trace metal distribution at the mining
communities at Talensi-Nabdam District of Upper East Region of Ghana were
modeled in this study. Development of the models was based on the novel idea that
there is a relationship between the fraction of metal associated with humic matter,
intrinsic properties of the humic matter and metal partition constant. A quantitative
account of the role of humic substance in metal distribution was studied using
component factor analysis approach to model the speciation and distribution
phenomena of trace metals at the selected ecosystem for the study. The properties of
humic substance and the interactions of trace metals were correlated and used to
develop mathematical models for the description of the role of humic substance in
metal partition. The conceptual and mathematical models were proved to have the
potential to explain the humic-impacted-partition of trace metals when they were fitted
to data obtained from field and simulation experiments. The distribution model
explained 97.99% of the factors which influence trace metal distribution in the
terrestrial environment out of which humic substances accounts for more than 30 % of
all the factors. The speciation model also showed that humic substances account for
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13.06% of the variables which determine trace metal speciation at the ecosystem
studied. It was concluded that humic substances play a significant role in trace metal
distribution in terrestrial environment. The mathematical models gave good
correlations and R2 values when fitted to data from simulation experiments. The
models described the trace metal partition well in terms of humic acid (HA)
complexation and partition. The overall impression of the models is that HA influences
Cu distribution in soil solution system to an extent determined by the relative
proportion of other cations which compete with the metal for both the humic acid and
the soil mineral. The models also indicated that modification of the solid phase by HA
introduces two major heterogeneous binding sites in the solid phase (i.e., the organic
and inorganic binding sites) and that changes in the relative moles of the site types are
determined by the cation binding and hydrophobic properties of HA. The models
indicated that the properties of humic substance which makes it capable of influencing
trace metal distribution are hydrophobicity, detergent properties and metal complexing
ability.
Description
A thesis submitted to the Department of Chemistry, Kwame Nkrumah University of Science and Technology in partial fulfillment of the
requirements for the degree of DOCTOR OF PHILOSOPHY.